1. Field of the Invention
The invention relates to borosilicate glass and also to uses of the glass.
2. Description of the Related Art
The group of the borosilicate glasses is extremely extensive. The representatives of this group have the following basic composition range in common:    SiO2, approx. 70 to 80 percent by weight,    B2O3, 7 to 20 percent by weight,    Al2O3, 2 to 7 percent by weight,    Alkali metal oxides, 3 to 10 percent by weight.
The glasses contain aluminum oxide in order to improve their resistance to devitrification and the chemical resistance.
However, glasses of this type release aluminum ions to a wetting aqueous liquid, which is disadvantageous for certain applications. For example, aluminum is currently suspected of harming the health of people of corresponding disposition. In such cases, therefore, conventional primary pharmaceutical packaging materials made from glass are relatively unsuitable for the administration of injectable substances.
Furthermore, aluminum oxide increases the melting and working points of the glasses considerably, increasing the energy consumption involved in the production processes.
The physical and glass-technical properties influenced by Al2O3 generally cannot be reproduced by simply replacing the aluminum oxide with one or more other constituents. Rather, completely new developments or extensive changes to the glass composition are required.
Standard borosilicate glasses are distinguished by their high chemical stability and their high ability to withstand temperature changes. They have a low coefficient of thermal expansion.
On account of these properties, they are used in particular as ampoules and vials in the pharmaceutical industry for packaging, for example, injection preparations, for apparatus and equipment used in the chemical industry, both in production and on a laboratory scale, or as lamp glasses.
There is extensive patent literature concerning glasses of this type.
For example, DE 42 30 607 C1 describes chemically highly resistant borosilicate glasses which can be fused to tungsten. According to the examples, the glasses have working points VA>1210° C.
The borosilicate glasses described in German Laid-Open Specification DE 37 22 130 A1 also have high working points. Although the glasses belong to the first hydrolytic glass, they are relatively susceptible to crystallization, on account of the absence of K2O in these glasses.
The Li2O-containing glasses described in German Patent DE 195 36 708 C1 are also highly chemically stable but also have disadvantageously high working points.
The glasses described in German Patent DE 44 30 710 C1 have a high SiO2, content, namely >75 percent by weight and >83 percent by weight of SiO2+B2O3 in combination with an SiO2/B2O3 weight ratio of >8, which means that they are chemically highly stable but also have excessively high working points.